This invention relates generally to braking apparatus and more particularly to a brake that provides a holding torque sufficient to directly constrain the output torque of a rotary device.
Two types of electric brakes are generally known and commonly used with rotary devices such as electric motors and the like. One comprises the magnetic solenoid type brake, and the other comprises the less commonly used magnetic particle brake.
The solenoid brake typically functions to disengage the brake and employs a magnetic coil and an electrical energizing circuit to lift a spring-loaded abrasive clutch away from a reaction pad. To engage the brake, for example, the magnetic field is deenergized, allowing a bias spring to press the clutch against the reaction pad and lock the brake in place.
The magnetic particle brake, on the other hand, is constructed with a magnetic coil and a magnetic circuit which has a predefined gap in the flux return path. A fluid or powder with a heavy mixture of magnetic stainless steel particles is placed in the gap of the flux return path. When the magnetic coil is activated, the magnetic flux crosses the gap in the return path and lines up the magnetic particles such that the brake is locked. When the magnetic field is relaxed, the magnetic particles are demagnetized and again become part of the fluid or powder, as the case may be.
While such apparatus works extremely well for certain applications, the magnetic solenoid brake has certain limitations with respect to the holding torque which it can generate and therefore often requires the additional use of a transmission device such as a harmonic drive in order for it to operate as intended. This, however, limits its use options and restricts packaging. Since this type of brake operates upon generating a frictional hold, it can wear out with extended use.
The magnetic particle brake also is limited insofar as its holding torque is concerned. Also to power the magnetic particle brake a large and heavy magnetic circuit is required as well as an associated set of coils. The magnetic circuit and the coils are used directly to provide the braking torque and thus the power requirements and the heat build up can be considerable. Also, the magnetic particles through prolonged use tend to wear smooth, thereby diminishing its effectiveness. Moreover, it is cumbersome and complicated to construct the powder system and seals associated with it. For space applications, a magnetic fluid would not be acceptable.